Chairman Ben S. Bernanke has big shoes to fill this week when he speaks at the Federal Reserve’s annual symposium in Jackson Hole, Wyoming: His own.

Last year, Bernanke hinted that the Fed might embark on a second round of asset purchases to bolster the recovery, kicking off a 28 percent rally in the Standard & Poor’s 500 Index of stocks that ended in a three-year high on April 29.

Now, any boost to the economy from the Fed’s $600 billion of bond buying is hard to detect, with growth slowing to a less- than-1-percent annual pace in the first half, the U.S. losing its top credit rating from S&P and stocks falling about 18 percent from their peak.

The deterioration — coupled with a government that’s cutting spending and showed itself to be “dysfunctional” ahead of the debt-ceiling expiration this month — increases the pressure on the U.S. central bank to show it can and will help expansion, according to Neal Soss, chief economist at Credit Suisse Holdings USA Inc.